1. University of Jordan – School of Medicine
GI embryology 2
Fareed Khdair , MD
Assistant Professor
Chief, Section of Pediatric Gastroenterology, Hepatology, and Nutrition
University of Jordan – School of Medicine

2. Clinical Outline Lecture one : Lecture Two ( next week ):
Gut formation
Foregut:
esophagus, stomach, Duodenum
Liver , gall bladder and pancreas
Spleen
Lecture Two ( next week ):
Mid gut : duodenum . Jejuno-ileum, colon
Hind gut : distal transverse colon – anal canal
Clinical

3. GI embryology

4. References
Lecture slides
Langman medical embryology
Chap 15

5. Case 1
vomiting

6. Normal
malrotation

7. Mid Gut

8. Mid gut
begins distal to the entrance of the bile duct into the duodenum
terminates :junction of the proximal 2/3 of the transverse colon with the distal third.

9. Midgut
communicates with the yolk sac by way of the vitelline duct or yolk stalk
supplied by the superior mesenteric artery
Development characterized by rapid elongation :primary intestinal loop

10. Growth phases of mid gut
Herniation – physiologic 6th week
Rotation 90 degrees
Retraction 10 th week
Further rotation 180 degrees

11. Mid gut growth
The cephalic limb of the loop develops into: the distal part of the duodenum, the jejunum, and part of the ileum.
The caudal limb becomes the lower portion of the ileum, the cecum, the appendix, the ascending colon, and the proximal two-thirds of the transverse colon.

12. Mid gut
WAPWON.COM_Embryological_Rotation_of _the_Midgut.mp4

13. Physiological Herniation
At 6 Weeks
Due to :
rapid growth of the liver.
Rapid growth of intestinal loops
the abdominal cavity becomes too small
they enter the extraembryonic cavity in the umbilical cord

14. ROTATION OF THE MIDGUT
rotates around axis of superior mesenteric artery
Counterclockwise
approximately 270◦ when complete
Rotation occurs :
during herniation (about 90◦)
during return of the intestinal loops into the abdominal cavity (remaining 180◦)

15. during mid gut rotation
Small intestine :
elongation
jejunum and ileum :coiled loops
large intestine :
Elongation
No coiling

16. Retraction
During the 10th week, herniated loops return to the abdominal cavity.
Due to :
reduced growth of the liver
and expansion of the abdominal cavity
The proximal portion of the jejunum, the first part to reenter the abdominal cavity, comes to lie on the left side
The later returning loops gradually settle more and more to the right.

17. Retraction
The cecal bud is the last part of the gut to reenter the abdominal cavity.
Temporarily it lies in the right upper quadrant

18. Appendix embryology Forms a s as a narrow diverticulum form cecal bud
its final position frequently is posterior to the cecum or colon.
These positions of the appendix are called retrocecal or retrocolic

19. Mesenteries of intestinal loops

20. Dorsal and ventral mesentry

21. Mesentery proper The mesentery of the primary intestinal loop.
changes with rotation and coiling of the bowel.
1- caudal limb of the loop moves to the right side of the abdominal cavity.
2- the dorsal mesentery twists around the origin of the superior mesenteric artery

22. Cross sectional view

23. Retro Vs intraperitoneal
After fusion of these layers:
the ascending and descending colons are permanently anchored in a retroperitoneal position
The appendix, lower end of the cecum, and sigmoid colon: retain their free mesenteries
( intraperitoneal structures)

24. Sagittal view of gut mesenteries

25. transverse mesocolon
It fuses with the posterior wall of the greater omentum but maintains its mobility.
Transverse colon: intraperitoneal organ

26. Small bowel mesentery
The mesentery of the jejuno-ileal loops is at first continuous with that of the ascending colon
Then obtains new attachment line : small bowel becomes intraperitoneal

27. Congenital anomalies of mid gut

28. Malrotation Anti clock wise roation for 90◦ only.
When this occurs, the colon and cecum are the first portions of the gut to return from the umbilical cord, and they settle on the left side of the abdominal cavity
resulting in left-sided colon.
Results in recurrent vomiting and abdominal pain
twisting of the intestine (volvulus) compromise s the blood supply.

29. Reversed rotation primary loop rotates 90◦ clockwise
In this abnormality the transverse colon passes behind the duodenum and lies behind the superior mesenteric artery.
Symptoms usually occur early in life

30. Gut Atresias and Stenoses
Atresias and stenoses may occur anywhere along the intestine
Most occur in the duodenum, fewest occur in the colon, and equal numbers occur in the jejunum and ileum (1/1500 births).
Atresias in the upper duodenum are probably due to a lack of recanalization

31. Body Wall Defects Omphalocele Gastroschisis

32. Omphalocele
herniation of abdominal viscera through an enlarged umbilical ring.
The viscera are covered by amnion.
Due to failure of the bowel to retract
occurs in 2.5/10,000 births
associated with a high rate of mortality (25%)
Associated with severe malformations, such as cardiac anomalies (50%) and neural tube defects (40%).
Approximately half of live-born infants with omphalocele have chromosomal abnormalities.

33. Gastroschisis
is a herniation of abdominal contents through the body wall directly into the amniotic cavity.
It occurs lateral to the umbilicus usually on the right
Not covered with amnion
Not associated with other anomalies

34. Vitelline duct abnormalities

35. Hind Gut

36. Case 1
No meconium

37. Imperforated anus

38. Hindgut
gives :
the distal third of the transverse colon,
the descending colon,
the sigmoid,
the rectum,
and the upper part of the anal canal.
The endoderm of the hindgut also forms the internal lining of the bladder and urethra
( from Allantois)

39. Definitions The cloaca :
an endoderm-lined cavity covered at its ventral boundary by surface ectoderm.
Cloaca membrane:
Membrane between hindgut endoderm, and ectoderm
Gives rise to anal canal and urogenital sinus openings
Allantois :
ventral extension of the hind gut
Gives the uro-genital sinus
urorectal septum
A layer of mesoderm,, separates the region between the allantois and hindgut.

40. Hind gut embryology
The terminal portion of the hindgut enters into the posterior region of the cloaca : the primitive anorectal canal
the allantois enters into the anterior portion :the primitive urogenital sinus

41. Hind gut embryology end of the 7th week: cloacal membrane ruptures:
Dorsal : anal opening for the hindgut
ventral opening for the urogenital sinus.
The perineal body : the tip of the urorectal septum forms
proliferation of ectoderm closes the caudal region of the anal canal.
During the 9th week, this region recanalizes

42. Embryology of anal canal
distal part :
originates in the ectoderm.
Stratified squamaous epithelium
supplied by the inferior rectal arteries ( branches of the internal pudendal arteries)
Proximal part :
Endoderm
Coloumnar epithelium
Supplied by superior rectal arteries ( br. Inferior mesenteric artery )
Junction : pectinate line

43. Hind gut abnormalities

44. Summary
WAPWON.COM_10- _The_development_of_the_gastrointestinal_ tract.mp4

46. The End

47. Questions?